Traditionally, airplanes have incorporated a variety of instrument gauges to indicate various parameters of flight to a pilot. The most basic of these traditional instruments are four gauges arranged in a traditional “T”, pattern, and include airspeed, attitude, altitude, and directional indicators. Other gauges such as climb and flight path deviation indicators are also common, and are usually positioned near the basic “T” instrument cluster.
As mechanical gauge technology has been replaced with electronic and computerized flight indicator displays, integration of several of these traditional data elements onto one screen has become common, and displays such as liquid crystal displays (LCDs) have been configured to show a wide variety of flight data on a relatively small number of LCD screens. These screens can vary from airplane type to airplane type, and even between individual airplanes depending on the sensors and navigational systems installed on each aircraft.
Because the pilot must take his eyes away from the aircraft's canopy or windshield and scan the instruments from time to time, certain flight data is sometimes integrated and displayed via a head-up display (HUD). This HUD technology provides projection of an image onto the windshield or canopy, or onto a semitransparent eyepiece in the pilot's helmet to present information to the pilot without requiring looking down at an instrument cluster.
In some applications, traditional flight data such as glide slope, flight path deviation, and attitude indicators are incorporated into the HUD, while in other applications such as military applications the HUD displays are used for nontraditional applications such as target tracking. In both cases, the goal is to provide the pilot with data while eliminating the need to look away from the windshield toward an instrument cluster.
The image that creates the head-up display is typically projected from a cathode ray tube (CRT), much like those found in a traditional television set or computer monitor. The image to be projected is displayed on a CRT that is carefully positioned such that the image reflects off the windshield, canopy, or other semi-reflective reflector element in the pilot's helmet, thereby creating a visible image that is projected over the still-visible view through the pilot's helmet or windshield.
The CRT will desirably have a certain level of brightness in the image it produces, so that the image it creates is clearly visible on the reflector's semi-reflective surface but does not obscure viewing behind the reflector. Other factors that must be considered in designing a HUD display include the amount of weight and size required, especially for helmet-mounted displays that the pilot must support when wearing the attached helmet. This makes it desirable to utilize whatever display technologies can provide the desired brightness, resolution, and other required characteristics at the lowest weight, size, and cost.
It is therefore desired to reduce the weight, cost, and size of head-up display devices, particularly when applied to helmet-mounted head-up displays.